Motor controller



Jan; 30, 1945. E, MOYER 2,368,485

MOTOR CONTROLLER Filed Dec. 1, 1942 Inventor: Elmo E. MO 6T,

e Hi S Attorney.

Patented Jan. 30, 1945 MOTOR CONTROLLER Elmo E. Moyer, Scotla, N. Y., assignor to General Electric Company, a corporation of New York Application December 1, 1942, Serial No. 467,501 12 Claims. (on. ire-28s) This invention relates to control systems, more particularly to systems i or controlling the opera tion of electric motors, and it has for an object the provision of a simple, reliable, and improved control system of this character.

More specifically, the invention relates to systems for controlling the starting of an electric motor, and a further object of the invention is the current supplied to the armature to a preto accelerate the motor at the maximum permissible rate to a desired speed which may be preset upon a calibrated speed control device.

Another object of the invention is the provision of a control system in which the current is limited to a predetermined value thereby to accelcrate the motor to the preset speed without excessive current peaks.

Another object of the invention is the provision'of simplified and improved controlling circuits and apparatus for increasing the voltage supplied to the armature of the motor sufficiently to compensate for the internal voltage drop of the armature of the motor.

A further object of the invention is the provision of a wide, steple'ss range of operating speeds.

A still further object of the invention is the provision of a compact variable speed motor drive supplied from a source of alternating voltage in which gears, pulleys, clutches and bulky apparatus heretofore used are eliminated, and in which the objects set forth in the foregoing are achieved largely by the use of inexpensive electronic devices.

In carrying the invention into effect in one form thereof, a direct current motor is supplied through a transformer and asuitable electric valve apparatus from a source of alternating voltage. For the'purpose of presetting a desired operating speed of the motor, a device which is calibrated in terms of speed produces 8. reference voltage corresponding in magnitude to a desired operating speed, and means are provided for producing a control voltage which is dependent upon the speed of themotor. The difference of these two voltages is applied to the cathode and control grid of a second electric valve apparatus which is connected to control the first electric valve apparatus to accelerate the motor to the desired operating speed. Also, means responsive to the anode current of the first electric valve apparatus are provided for adding a voltage in the cathode circuit of the second electric valve apparatus whichcontrols the first electric valve apparatus to increase the voltage supplied to the motor armature sufflciently to compensate for its internal voltage drop. To limit determined value, a thirdelectric valve means is provided which responds to a predetermined value of current in the anode circuit of the first electric valve apparatus to apply a sumciently negative voltage to the grid of the second electric valve-apparatus.

Another feature is the provision of additional electric valve means which respond only to arms. ture voltages which are in excess of a predetermined value for weakening the field of the motor thereby greatly to extend the speed range of the motor beyond the range which is obtainable by variation of the armature voltage.

For a better and more complete understanding of the invention, reference should now be had to the following specification and to the accompanying drawing, the single figure of which is a simple, diagrammatical illustration of an embodiment of the invention.

Referring now to the drawing, an electric motor ill having an armature lilo and a shunt field winding lllb is supplied from a source of alternating voltage ll through a supply transformer l2 and suitable electric valve apparatus comprising valves l3, i4, i5, and IS. The starting, stop ping, and reversing of the motor iii are under the control of a suitable controlling accessory,

such as a push button station 51 and a speed controlling rheostat l8. If desired, the speed controlling rheostat is may be mounted on the push button station control panel.

The secondary winding of the supply transformer i2 is provided with a mldtap I21: and this midtap is-connected to the bus is which becomes the negative side of the direct current system, i. e, the negative armature terminal, the negative field terminal, and the negative control terminal.

Suitable nonlinear resistance units 26 and 2i are connected across each half of the secondary winding. These nonlinear resistances may be made of any suitable material having a nonlinear characterlstic, but are preferably made of acomposition of silicon carbide crystals which are held together by a suitable binder. Resistance material of this character is sold on the market under the trade name Thyrite, and is described and claimed in United States Patent 1,822,742, Karl B. McEachron, dated September 8, 1931. The purpose of these nonlinear resistances is to protect the inductive winding from high voltage surges which sometimes occur in tube circuit operations. The nonlinear resistance provides a low resistance shunt path to voltages transformer i2. The filamentary cathodes lib and Hib are heated by means of current supplied to the cathodes through a filament transformer, the secondary windings 24a and 2422,01 which are shown connected to the cathodes, and the primary windings of which are not shown in the drawing. It will be understood that the primary winding of the filament transformer may be connected to low voltage taps of the secondary wind ing of the supply transformer 12. These secondary windings 24a and 24b are inidtapped, and

the midtaps are connected to the conductor 25 which thus becomes the field supply. 1

The supply of voltage from the source H to the armature Illa oi the motor is controlled by positive terminal of the means of the electric valves l3 and it. As shown.

the electric valves 13 and it, like the electric valves I5 and ID, are connected for bi-phase rectification, i. e., their anodes l3a and Ma are connected through primary windings 26a and 26b of a special control transformer 26 and through contacts 21a and 21b oi anode contactor 21 to opposite terminals oi the secondary winding of the supply transformer II. The cathodes I32) and llb of valves 13 and II are provided with suitable heating units which are connected to the secondary windings 24c and 24d of a filament transformer. The cathodes lab and b are connected by means of conductors 28 and 29, respectively, to the terminal 30 which thus becomes the positive side of the supply for the armature.

Although the electric valves i3, i4, i5, and It may be of any suitable type, they are preferably grid controlled, mercury vapor thyratron tubes. The valves I3 and H are provided with shield grids I3c and Me as well as with control grids Nd and lid, respectively. The valves i5 and I8 which control the supply of current to the field winding have directly heated filamentary cathodes and have only single grids 15c and IE0 which are the control grids. In thyratron valves, the function 01' the control grid is only to initiate the flow of current between the anode and the cathode during each positive half-cycle of anode voltage. Once current has started to flow, the grid exercises no further control until the conductivity of the ,valve has been interrupted by some means external to the valve itself. Once the current has ceased to flow, the potential of the grid will again determine the point in the positive halt-cycle of anode voltage at which the valve will again become conducting. These valves are therefore grid controlled arc rectiflers.

If desired, a time delay relay (not shown) may be provided to prevent the application of power to the anode circuit for an interval of time suiiicient for the initial heating 0! the cathode oi the electric valve. Also, a field protective relay (not shown) may be provided for the purpose of preventing the application oi. voltage to the armature or the motor until a safe field excitation has been established and for interrupting the armature circuit in the case oi. field failure. Time delay devices and field protective relays of this character are well understood devices and ascacss for this reason they are omitted from the drawing.

Although the thyratron valves 83 and it may be controlled by any suitable method, it is preferred to use,the method of phase shift control of the grid voltage. For the purpose oi carrying out this method of control, a phase shifting network is provided. This network comprises a resistor 3| and the alternating current winding 32a of a saturable core type reactor 32. Another phase shifting network is provided for controlling the field thyratrons I5 and I B. This network comprises a hired resistor 33 and a capacitor 3|. The phase shifting network for the field thyratrons is connected directly across the low voltage taps 35 and 36 of the supply transformer, whereas the network for the armature thyratrons l3 and I4 is connected across the low voltage taps through the normally closed contacts of the stop push button switch 31. The primary winding 38a of a gridtransformer 38 is connected between the midtap l2a of transformer i2 and the junction point 3hr of the resistor 3| and reactor winding 32a. This grid trans former has two secondary windings 38b and 380. The secondary winding 38b is connected between the cathode and grid 01. the armature thyratron i3, and similarly, the secondary winding 38c is connected between the cathode and grid of the armature thyratron H. A corresponding grid transformer 39 is provided for the field thyratrons i5 and i 5 which has a primary winding 39a connected between the midtap Ila of transiorrner i2 and the junction point 33:; of the re sistor 33 and the capacitor 34, and a pair of secondary windings 39b and 380 which are connected in the grid circuits of the field thyratrons i5 and i8, respectively. The phase shift oi the grid voltages of the armature thyratrons is produced by varying the reactance oi the saturable core reactor 32, which is controlled by varying the direct current saturation of this reactor. The control issuch that when the saturable reactor is saturated, the voltage of the grid transformer tends to be in phase with the anode transiormer voltage and when the reactor is unsaturated, the voltage of the grid transformer tends to be out of phase and lagging. Intermediate values of saturation produce intermediate phase relationships. Thus, when the saturable reactor 32 is fully saturated, the thyratrons l3 and M are fully conducting and conversely, when the reactor is unsaturated, the thyratrons- I3 and H conduct a minimum amount o1 current. For in termediate values of saturation, the thyratrons l3 and I4 have corresponding intermediate values of conductivity.

The push button station I! is provided with a pair of push button type switches 40 and 3'! ior controlling the starting and stopping of the motor I 0.

Voltage for control purposes, i. e., controlling the operation of the electric valves of the system, is supplied to a positive control voltage bus Ii by means oi a double diode rectifier valve 422 whose anodes Ma and 42b respectively connected to opposite terminals of the secondary winding of the supply transformer i2 and whose cathodes are directly connected to the positive control bus ll. Since the bus 15 is connected to the midtap lilo oi the supply transformer, the bus 19 therefore serves as the negative control bus.

The saturation of the saturating winding 32!) of the armature control saturable reactor is aeeaees their anodes 43a and 44a connected to the opposite terminals of the secondary winding of the supply transformer and have their cathodes 43b.

and 442) connected through opposite halves 26c and 26d of the secondary winding oi the special control transformer 26 to one terminal of the saturating winding 32b of the saturable reactor 32, the opposite terminal of which is connected through contact 270 to the positive terminal 30 of the motor armature Illa. The grids 43c and ride of both valves are connected through a re? sistor 827 to the slider 18a of the preset speed controlling rheostat 58. Thus, the valves 43 and 4t serve to compare the armature voltage of the motor in with the reference voltage which is set on the speed controlling rheostat l8 and to apply the difierence of these two voltages to the saturating winding 3%. In addition to serving as controllers of the current supplied to the saturating winding 321), the valves 43 and 44 also serve to rectify this voltage which has both A. C. and D. C. components, and act to prevent a reverse current flow through winding 32b.

Consequently, ifthe armature voltage should rise above the value of voltage preset on the-speed controlling rheostat 18, the valves 43 and 44 become nonconducting and thus prevent the rise in armature voltage from saturating the saturating winding and producing a runaway condition. It will be understood that the valves 43 and 44 may be combined in a single envelope to constitute a twin triode valve.

For the purpose of accurately maintaining the speed of the motor at the level which is preset upon the speed controlling potentiometer l8, means are provided for compensating for the RI drop in the armature circuit. In efiect,

these means subtract an increment of voltage from the armature terminal voltage so that the resultant voltage which is used as a signal of speed is approximately equal to the countervoltage of the motor. That is to say, to hold constant armature countervoltage is to hold constant speed, and this is possible when the voltage supplied to the armature terminals is increased by an amount equal to the RI drop of the armature circuit.

The secondary windings 28c and Mid of the anode transformer 26 serve to subtract the increment of voltage from the terminal voltage of the motor. These secondary windings introduce voltages into the cathode circuit of whichever of the valves 43 or 44 is active at the instant in opposite sense to the armature voltage. Thus, during the half-cycle of anode voltages in which both the armature thyratron l3 and the valve 43 are conducting, a pulse of voltage is induced in the secondary windings 26c and 26d which produces potentials having the polarity indicated and during the succeeding halfcycle, potentials of the reverse polarity are" produced. The secondary windings 28c and 26d are loaded by means of a variable resistor 45. For a given ratio between the primary windings 28a,

43 and 44 become sufllciently less positive or more negative than the cathodes 43b and 44b to decrease the saturating current in winding 32b and establish an equilibrium condition. It is thus seen that the average voltage from the negative armature terminal l9 to the cathodes 43b and 44b is a measure of the countervoltage of the motor which is a true measure of speed of the motor.

For the purpose of limiting the armature cur rent to a maximum permissible value, means are provided for decreasing the voltage of the grids 43c and 440 in response to a given current signal and thereby to cause the armature voltage to be decreased. These means comprise an additional pair of triode valves 3b and i? having their anodes 56a and 41a directly connected by means of the conductor 48 to the grids Ne and 440 of valves 43 and 44, and having their grids 46b and 41b connected to the negative control bus l9 through a grid resistor 48a and having their cathodes 46c and 4'lc connected through opposite halves 26c and 25f of an additional secondary winding of the transformer 293 to the positive control bus 4!. During the pos itive half-cycle of anode voltage in which the ar mature thyratron i3 is conducting, voltages wiii be induced in the secondary windings 26c and 26! having the polarity indicated in the drawing. During the succeeding half-cycle when the armature thyratron i4 is conducting, these induced voltages in the secondary windings 25c, 26} will have the opposite polarity.

V the midtapped secondary windings 25e, 28f, a

voltage equal to hair the total secondary voitage alternately tends to decrease the voltage or" cathodes 48c and 410. However, as long as the peak value oi these added voltages in the oathode circuits is less than the value of the voltage from the negative bus E9 to the positive control bus 4i, the valves t8 and 41 will be noneonducting. However, when these secondary induced voltages equal or exceed the voltage across the control busses, the voltages of the cathodes die and 410 will alternately become more negative than the voltages of their grids and the valves 45 and 41 will be alternately conducting and will decrease the grid voltage of valves 43 and 44 by virtue of the current drawn through resistor 'ieb, thereby to cause the armature voltage to decrease accordingly, because the saturating windnected across the armature lfla of the motor, and

a similar voltage divider comprising resistors 59 and 5! in series relationship with each other is connected across the control voltage busses 4i and IS. The junction point of the secondary windings 39b and 390 of the grid transformer of the field thyratrons l5 and i6 is connected through a resistor 52 to the positive control voltage bus 4| and through a conductor 53, the valve 54, and resistor 5| to the negative control voltage bus I9. Thus there is applied to the grids of the field thyratrons I5 and IS a positive direct current bias voltage by means of the valve 54 in series with a degree lagging alternating current component of voltage which is induced in .l! are phased full on."

the secondary windings 38b and 39c by the p mary winding 39a. Thus, the field control thyratrons l5 and is are phased full on until the average field voltage becomes greater than the voltage between the negative control bus I9 and the neutral point of the secondary windings 38b, 38c of the grid transformer at which point, an equilibrium condition exists. The control grid of the valve 54 is connected tothe junction point between the resistors 49 and 49a which comprise the voltage divider connected across the armature Illa ofthe motor. When the voltage of the grid Me of the valve 54- is more negative than the voltage of the cathode 54b, the valve 54 is nonconducting, the voltage drop across the resistor 52 is zero, and the field thyratrons I5 and The phase control of field thyratrons I5 and i6 by means of tube 54 is for the purpose of automatically weakening the motor field after the armature voltage has reached a predetermined valuewhich is deter mined by the comparison of the ratios of resistor 49 to resistor 9a and resistor 5| to resistor liil. If the armature speed adjusting rheostat it preset for a higher armature voltage, the field will be weakened and the speed increased, all uuder the control of the single speed odjusting rlico-- stat l8.

With. the foregoing understanding oi? the ole -ments and their organization the completed system, the operation oi the system itself will readily be understood from the roilowino; detailed description:

Assuming that it is desired to opcmte "the o1otor at a speed above base within the field weakened range, the knob of "the speed c trolling potentiometer is moved until the 18a is at a position such as lndlcutcd in the tire. ing. Further ossuming that the primary oil supply transformer 12 is energized or conuec of the primary winding to u sour o field thvrutrons I5 and ill will he as explained in the foregoing ouo W." ing maximum excitation the hold it To start the motor, the uteri; push out depressed to bridge the norms o ouch V 0a thereby to complete all sno the operating coil of the anode coma or i the low voltage tap 35 through uomioily i contacts of the stop push button ill, contocto the start push button it, and operotiog coll oi the anode contactor 21 to the opposite low volt 36. In response to energioation, ouode con 21 closes its normally open contucto 27d to coinplete a sealing-in circuit for the coil oi c on tactor in parallel with the contccis of the to push button switch 40 which. now they he rolled Simultaneously, the anode contoctor chines main contacts 21a and 21b to comulete the nections from the anodes i302 and [Mo oi the mature thyratrons l3 and H to the opposite l minals of the secondary winding or the supply transiormer l2. Simultaneously, the anode tontactcr 21 closes its contacts Mo to complete tho connections of the saturating winding can of the armature satin-able reactor 32 to the bus 28 to which the positive terminal 30 of the armature Illa of the motor is connected. At the instant before the closing of contacts 210, the saturable reactor 32 is fully desaturated and thus the reactance of its reactance winding 32a is maximum. The result is that the phase of the grid voltage of the armature thyratrons II and I4 is fully retarded and thus the armature current is allowed to build p at a time rate determined by the inductance of the direct current saturating windin 3% of the armature saturable reactor. If the grid voltage of the armature thyratrons were fully advanced when the contacts of the anode contactor were closed, the armature current .for the first few cycles might be undesirably high until sufllcient voltage had been built up through the anode current transformer circuit to initiate operation of the current limiting feature of the control.

As a result of the completion of the anode circult of the armature thyratrons l3 and I4 and the energization of the direct current saturating winding 3222 or the armature saturable reactor, the motor begins to accelerate to a speed determined hy the setting of the speed control potentioineter It. During acceleration, before the anmature countervoltage has built up to a value corresponding to the preset speed which it is desired to maintain, the phase of the grid voltage of the armature thyratrons tends to be fully advanced and hence. the armature thyratrons tend to supply a current to the armature which is several times full lood value. However, the current limiting control acting through the special control transformer 26, the valves 15- and ll, and valves t3 ond M, decreoses the output of the armoturo thyrotrous to the value determined by the relation oi the current in the loilmorxr windthe special control transformer the voltog'e induced the secondary wiodiiflgs 26c and ow minted out in the foregoing, the voltage applied to the saturating winding Mb o soturohle reactor tilt is the di;

c-e voltage which is or 131113QllliltBIltiOIilEtEl it. Tl s, its countervoltuge loco ce voltage whici'i is ooollct to excite tiug villidh'lg llllll to h sic ooeed oi th the l o value such that with it oi the motor title void negative to cause vol'vc This produces on in ocross the resistor t current ueootive l we the field coding the pile-so oi" the orid Wltil lespect to the duode voltage. the lleld thyratrouo it and iii to th current supplied to the :i'leld winding "in," further to increase the speed of the lira, El lllhrium condition in the icl d "t u the difference voltoge oooiied the lttllilg winding 3% lust ouillcient the oeturchle reactor the amount o the motor to operate ot o *d corresponding to the setting oi" the poiioroetcr it".

he voltage induced in the secondory wind ingo tile cud 26d of the anode-current tronsi ruler til renders voltages "the cathodes D d to illi one] its negative lay an amount proper subsequently open as a result of the deenergiza tion of their operating coils, the contacts of the anode contactor will not be required to interrupt any appreciable current. If desired, the anode contactor may be provided with normally closed contacts to complete a. dynamic braking circuit through a dynamic braking resistor in parallel with the armature when the anode contactor drops out; This of course results in producing a dynamic braking torque which. rapidly brakes the motor to rest.

Although in accordance with the provisions of the patent statutes this invention is described as embodied in concrete form and the principle.

thereof has been described, together with the best mode in which it is now contemplated applying that principle, it will be understood that the apparatus shown and described is merely illustrative and that the invention is not limited thereto, since alterations and modifications will readily suggest themselves to persons skilled in the art without departing from the true spirit of this invention or from the scope of the annexed claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. Apparatus for controlling an electric motor having an armature winding and a field winding, means for supplying current to one of said windings, electric valve means for supplying a pulsating rectified voltage to the other of said windings, means for producing a reference voltage corresponding in magnitude to a desired operating speed of said motor, means for producing a control voltage dependent on the speed of said motor, a second electric valve means provided with an anode, a cathode, and a control grid and having its grid and cathode'connected to be responsive to the difference of said control and reference voltages, means responsive to the current flowing in the anode cathode circuit of said second electric valve means to control the voltage supplied by said first electric valve means, and means responsive to the armature current of said motor for adding a voltageproportional to said armature current in the cathode circuit of said second valve means thereby to vary the voltage supplied to said other winding to compensate for the internal voltage drop of the armature of said motor comprising a transformer having its primary winding connected in the anode-cathode circuit of said first valve means and having its secondary winding connected in the anode-cathode circuit of said second valve means.

2. Apparatus for controlling an electric motor having an armature winding and a field winding, means for supplying current to on of said windings, electric valve meansior supplying a pulsating direct voltage to the other of said windings, means for producing a reference voltage corresponding in magnitude to a desired operating speed of said motor, means for producing a control voltage dependent on the speed of said motor, a second electric valve means provided with an anode, a cathode, and a control to be responsive to the difierence of said control and reference voltages, means-responsiveto the 'current flowing in the anode cathode circuit of said second electric valve means to control the voltage supplied by said first electric valve means, means responsive to the armature current of said motor for adding a voltage proportional to said armature current in the cathode circuit of said second valve means thereby to vary the voltage supplied to said other winding to compensate for the internal voltage drop of the armature of said motor comprising a transformer having its primary winding connected in the anode-cathode circuit of said first valve means and having its secondary winding connected in the anode-cathode circuit of said second valve means, and means responsive to the armature current of said motor for varying the grid voltage of said second electric valve means to limit the armature current of said motor to a predetermined value.

3. Apparatus for controlling an electric motor, means for supplying current to the field winding of said motor, electric valve means for supplying a pulsating direct voltage to th armatureof said motor, a source of reference control voltage, a second electric valve provided with an anode, a cathode, and a control grid and having its cathode connected to one terminal of said armature and having its grid connected to said reference voltage source so that the magnitude of the current transmitted between said anode and cathode is determined by the difference of the countervoltage of said motor and said reference voltage, means responsive to the current flowing in the anode cathode cir suit of said second valve means for controlling said first valve means to control the voltage supplied to said armature, and means responsive to said armature current for adding a voltage in circuit between said armature terminal and cathode thereby to control the voltage supplied to said motor to compensate for th internal grid and having its grid and cathode connected II voltage drop of the armature of said motor comprising a transformer having its primary winding connected in circuit with said armature and its secondary winding connected in the anodecathode circuit of said second electric valve.

4. Apparatus for controlling an electric motor, means for supplying current to the field winding of said motor, electric valve means for supplying a voltage to the armature of said motor, a source of reference control voltage, a second electric valve provided with an anode, a cathode, and a control grid and having its cathode connected to one terminal of said armature and having its grid connected to said reference voltage source so that the magnitude of the current transmitted between said anode and cathode is determined by the difference of the countervoltage of said motor and said reference voltage, means responsive to the current flowing in the anode cathode circuit of said second valve means for controlling said first valve means to control the voltage supplied to said armature, means responsive to said armature current for adding a voltage in circuit between said armature terminal and. cathode thereby to control the voltage supplied to said motor to compensate for the internal voltage drop of the armature of said motor, and means responsive to the armature current Of said motor for varying the grid voltage of said second electric valve means to limit said armature current to a predetermined value.

5. A motor controller comprising in comhlnaprovided with an anode, a cathode, and a contlon, means for supplying current to the field trol grid and having its cathode and grld con winding of a motor, electric valve means for nected to be responsive to the dlilerence or the supplying a pulsating voltage to the armature countervoltage of said motor and said terminal of said motor, means for producing a reference voltage for controlling the current transmitted control voltage corresponding in magnitude to between said anode and cathode, means res-pom the desired speed of the motor, a second electric sive to said current for controllin said first vvalve valve provided w a de a cat ode, and a means to control the voltage supplied to said control grid and having its cathode and grid armature, a current transformer having its pric ne t9d t b esp e to e e ce mary winding connected in the armature circuit the terminal voltage or said motor and said ref-- 0;? said motor and a second. winding n te crenoe v lta e for controlling the current now-- in circuit between said armature and sai cathing n the anode cathode circuit, means respon ode thereby to control said first valve means to sive to said current for controlling said first valve compensate for the internal voltage drop of said means to control the voltage supplied to said motor, said transformer having an, additional motor, and meamv responsive to the pulsating secondary winding and additional electric valve armature current of said motor for inducing a apparatus mm t t b responsive to th volt,- Voltage in the circuit between Said cat ode and age of said additional secondary winding to conan armatu e t i al f S d to f lJOIktrol the grid voltage of said second electric valve trolling d fi t Valve mfianfi t0 p ate for apparatus to limit the armature current of said the interval voltage drop of said motor. motor to a predetermined value.

6- A o or Controller comprising in wmbimlm 9. A motor controller comprising in oomhination. me for upply current to tho field tion, means for exciting the field or a motor, winding of amotor, electric valve mfians 01 Sl1pean for supplying a pulsating v nli agg p y a pulsating ge to the ar fl fl 0i armature of said motor comprising a first elecsaid motor, means for producing a reference m m apparatu prgvjdgd with an Flume, a control voltage corresponding in. magnitude to Cathode, and mntrm m means y the desir d spe d or th motor, s d elect-Flo th alternating voltages to said-gnu and some, val p v d d with an m a th da and. a a phase shifting network including o control grid and having its cathode and mid W mm Mammy T m with U, m connected to be responsive to the difference of for m the phasg mm m the terminal voltage or said motor and child o ivgl tageg 1* mm mlve m reference voltage for controlling "the ism-rent We mppiied in said m flowing i t anode c de C -h 111% a variable reference voltage con sponsive to said current tor controlling said mo 1mm m th degflgfl m r3 valve means to ClJIttlUl the voltage supplied, in 1 said motor, means responsiv to the "ouisot m m o m mm mm the armature current of said moto r inducir motor comm ing a m o, M w o Voltage n e c u bot rotor; orovid with on onode, c. on armature terminal f d. motor ll 1 control grid and havi; grid a trolling said first valve means to compenso, a mm m t the internal voltage drop means responsive sai controlling the grid voltog o. trio valve means to limit sum to a predetermined value.

tion, means for solving current to the to. motor, electric vo. o means for ou onlvin t sating direct voltage to the armature of tor, means for producing a reference voitogr responding in magnitude to the desired soared oi the motor, a second electric valve apparatus provided with an anode, a cathode, and a con- 10. A motor controller mmpr trol grid and having its cathode and grid coo. w igloo, means for exciting the nected to be responsive to the diii'erenco oi the countervoltage or said motor and sold tern al armature oi said motor compri log a voltage for controlling the current transm uteri trio valve apparatus provided 2 between said anode and cathode, means res-n 1-- oathode, and a control grid, Insane sive to said current for controlling said first valve m alternating voltages to said grid no means to control the voltage supplied to said phase ohiftino network. including a soto or n 1 error. ionoier' having .c .r anode chrcuit of armature, and a current transformer having its reactor provided with o. saturating Win primary winding connected in the armature o varying the phase relationship oi orio cult of said motor. and a. secondary winding con anode voltages oi said valve to control the volt nected in circuit between said armature and said B one supplied to said armature, means for Lomcathode thereby to control said first valve means duclng a variable reference voltage corresponding to compensate for the internal voltage drop of in magnitude to the desired speed of motor, said motor. means for supplying a variable direct lz'lurrent to 8. A motor controller comprising in combinamid stjttumting winding t vary th mugged f aid 1 means f r supplying current to h fi of m motor comprising a wcond electric valve opos- & mo electric valve mew-5 1'01 pp g ratus provided with an anode, a cathode, and a pulsating direct voltage to the armature of said control grid and having its grid and cathode conmotor, mea for nroduoinz a reference voltage nected to be responsive to the difference 01' said corresponding in magnitude to the desired speed reference voltage and the countervoltage or said of the motor, a second electric valve apparatus motor, means for supplying to the cathode of said second valve apparatus a voltage that is negative with respect to the voltage of its grid thereby to increase the voltage supplied to said armature to compensate for the internal voltage drop of said armature comprising a current transformer having its primary winding connected in the anode circuit of said first valve apparatus and a secondar winding connected between said armature and the cathode of said second valve apparatus, said transformer having an additional secondary winding and additional electric valve apparatus connected to be responsive to voltage of said additional secondary winding to control the grid voltage of said second electric valve apparatus to limit the armature current of said motor to a predetermined value.

11. A motor controller comprising in combination, electric valve apparatus for supplying a voltage to the armature of the motor, means for sup plying current to the field of said motor comprising a second electric valve apparatus provided with an anode, a cathode, and a control grid, means for producing a reference voltage corresponding in magnitude to a desired value of speed of said motor, means for producing a control'voltage dependent upon the speed of the motor, means responsive to the difference of said voltages for controlling said first electric valve means to control the'voltage supplied to said motor, and'means responsive to the speed of said motor only in excess or a predetermined value for controlling the grid voltage of said second electric valve means to decrease the current supplied to said field winding thereby further to in crease the speed of said motor.

12. A motor controller comprising in combination, electric valve apparatus for supplying 8, voltage to the armature of the motor, means for supplying current to the field of said motor comprising a second electric valve apparatus provided with an anode, a cathode, and a control grid, means for producing a reference voltage corresponding in magnitude to a desired value of speed of said motor, means for producing a control voltage dependent upon the speed of the motor, means responsive to the difference of said voltages for controlling said first electric valve mean to control the voltage supplied to said motor, and means responsive to the terminal voltage of said motor in excess of a predetermined value for controlling the voltage of said grid to decrease the current supplied to said field winding thereby further to increase the speed of said motor.

ELMO E. MOYER.

CERTIFICATE OF CORRECTION.

Patent NoQ' 2,568Ji85- ELMO-E. MOYER.

January 30,. 19145.

It is hereby certified that error appears in the printed specification ofthe above numbered patent. requiring correction as follows: Page 6, first column,'. 1ine 21-, for interval read --internal--; and second column,

line 11, for "second" read --s.econdaryand that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in, the Patent Office. I

Signed and sealed this 1 th day of May, A. D. 1915-.

(seal) Leslie Frazer Acting Commissioner of Patents. 

